A number of signal devices are available for indicating that mail has been delivered to and/or picked up from a conventional R.F.D.-type mailbox. Typically, these devices are attached to the mailbox by bolts, screws or other means that permanently mark or damage the box. Moreover, conventional mailbox signal devices employ a rather intricate, yet flimsy multi-part construction that is prone to breakage after repeated use. And, quite often, available mailbox signalling mechanisms are poorly visible, which renders them largely ineffective.